The invention relates to a multi-part oil control ring for pistons of internal combustion engines, having two lamellae consisting of steel strips that have parallel walls, the working surfaces of which have a barrel-shaped asymmetrical shape, in each instance, having a vertex line that extends over the circumference of the lamellae, as well as having a spreading spring disposed between the lamellae, which presses the lamellae both axially against one of the walls of a ring groove in the piston, in each instance, and radially against the cylinder wall.
In order to prevent too much motor oil from getting into the combustion chamber, which not only results in high oil consumption but also has negative effects on the emission behavior of the engine, a sufficient tangential force of the oil control rings is required to produce a radial contact pressure against the cylinder wall and thereby a good oil control effect. However, this results in a high surface pressure against the working surfaces of the steel lamellae, and therefore a high friction power during engine operation. This friction power worsens the degree of effectiveness of the internal combustion engine and accordingly increases the fuel consumption. The design of the tangential force of the oil control rings is therefore always a compromise between minimal friction power and maximal oil control effect. All of the measures for reducing the friction power during engine operation, without reducing the tangential force, thereby facilitate the design of the oil control rings, i.e. improve the degree of effectiveness of the engine.
Accordingly, an attempt was made, for oil control rings of the type stated, not only to provide a special design of the spreading spring, but also to form the working surfaces of the lamellae in such a manner that these meet the aforementioned requirements. Among other things, working surfaces that run plane-parallel to the cylinder wall are known, as indicated in U.S. Pat. No. 3,738,668, as are working surface contours that are configured to be symmetrically barrel-shaped, as described in DE 36 38 728 A1. In this connection, multi-part oil control rings having symmetrically barrel-shaped working surfaces of the lamellae are mounted in the piston in any desired installation position, i.e. not oriented.
Asymmetrical working surfaces of oil control rings or piston rings are known from DE 38 33 322 A1, DE 43 00 531 C1, or DE 44 29 649 C2. These embodiments, however, relate only to individual rings, whereby information relating to possible installation positions with regard to multi-part oil control rings cannot be derived from the references.